It is particularly important in trauma cases where spinal injury is suspected to immobilize the cervical spine, or back. Failure to do so can cause permanent paralysis or death! This is part of EMT and paramedic training. In the field it involves moving the person's back as a unit with as many as 5 rescuers assisting, the application of a cervical collar (which can be improvised from duct tape and cardboard), and securing the victim to a solid-backed stretcher or long board.
EMTs trained in wilderness first aid have a technique for verifying that the spine has not been hurt ("clearing the cervical spine") when the victim is several hours or more from the hospital and evacuation may not be indicated. Without this technique it may be necessary to carry a suspected trauma victim out only to discover that s/he had no injury worthy of the effort and expense.
See also first aid